Effect of walnut wood and walnut green shell biochar on water retention status in a sandy soil

Drought and the resulting stress are one of the most important and common environmental stresses which limit agricultural production. Researchers have used organic amendments such as biochar to improve soil properties and reduce the effects of the undesirable stresses. The purpose of this study was to investigate the effect of using the provided biochar of walnut wood and walnut green shell on retention curve and hydraulic parameters of a sandy soil in completely randomized design. For this purpose, the biochar were produced at 400 0C for 2 h. The amendments (walnut wood and walnut green shell and their biochar) at 1 and 2 w/w% ratios (36 and 72 t ha-1, respectively) were mixed with soil sample in three replications and were incubated for 120 days in greenhouse conditions. The retention curve of the incubated soils was measured using sandbox and pressure plates apparatus. Statistical analysis showed that the applied biochar had significant effects on bulk density, porosity, stability of aggregates in wet sieving, and van Genuchten’s parameters (except residual moisture parameter). Application of 2% walnut green shell biochar led to 17% reduction in bulk density (17%) compared to the control and increased the total soil porosity. Application of 2% biochar had the highest effect on the soil water retention curve. Also, the addition of biochar significantly increased soil water retention at low tension and decreased the difference in soil moisture content between treatments. Since water retention curve in lower tension is affected by coarse soil pores and soil structure it could be concluded that addition of biochar improved soil structure and increased coarse soil porosity. Application of appropriate biochar as an amendment in agricultural soil can partially improve the physical and hydraulic properties of sandy soils in semiarid region.